hello, when I use `nvcr.io/nvidia/tensorflow:19.03-py2`

to convert a tf saved_model, some logs like:

```
2019-07-11 07:25:46.811638: I tensorflow/contrib/tensorrt/segment/segment.cc:434] Not a TF-TRT candidate, (Op type: Relu), (Op name: resnet_v1_50/conv1/Relu), (Reason: excluded by segmenter option)
2019-07-11 07:25:46.811716: I tensorflow/contrib/tensorrt/segment/segment.cc:434] Not a TF-TRT candidate, (Op type: MaxPool), (Op name: resnet_v1_50/pool1/MaxPool), (Reason: excluded by segmenter option)
```

why it shows in simple conv1 layer, `Relu`

and `MaxPool`

ops is not supported here? they are the supported ops in trt-tf docs.

```
2019-07-11 07:08:32.773873: I tensorflow/contrib/tensorrt/segment/segment.cc:696] No device assigned to segment 54
2019-07-11 07:08:32.773897: I tensorflow/contrib/tensorrt/segment/segment.cc:681] Segment 55: parent=resnet_v1_50/block4/unit_2/bottleneck_v1/conv3/BatchNorm/beta/read:
2019-07-11 07:08:32.773917: I tensorflow/contrib/tensorrt/segment/segment.cc:686] Segment 55 has only 0 nodes, dropping
2019-07-11 07:08:32.773943: I tensorflow/contrib/tensorrt/segment/segment.cc:681] Segment 55: parent=resnet_v1_50/block4/unit_2/bottleneck_v1/conv3/BatchNorm/gamma/read:
2019-07-11 07:08:32.773964: I tensorflow/contrib/tensorrt/segment/segment.cc:686] Segment 55 has only 0 nodes, dropping
2019-07-11 07:08:32.773990: I tensorflow/contrib/tensorrt/segment/segment.cc:681] Segment 55: parent=resnet_v1_50/block4/unit_2/bottleneck_v1/conv3/BatchNorm/moving_mean/read:
2019-07-11 07:08:32.774011: I tensorflow/contrib/tensorrt/segment/segment.cc:686] Segment 55 has only 0 nodes, dropping
2019-07-11 07:08:32.774037: I tensorflow/contrib/tensorrt/segment/segment.cc:681] Segment 55: parent=resnet_v1_50/block4/unit_2/bottleneck_v1/conv3/BatchNorm/moving_variance/read:
2019-07-11 07:08:32.774057: I tensorflow/contrib/tensorrt/segment/segment.cc:686] Segment 55 has only 0 nodes, dropping
```

`No device assigned to segment 54`

means what?

and logs like:

```
2019-07-11 07:08:34.901294: I tensorflow/core/grappler/optimizers/meta_optimizer.cc:621] Optimization results for grappler item: tf_graph
2019-07-11 07:08:34.901373: I tensorflow/core/grappler/optimizers/meta_optimizer.cc:623] constant folding: Graph size after: 828 nodes (-324), 968 edges (-329), time = 1109.96594ms.
2019-07-11 07:08:34.901398: I tensorflow/core/grappler/optimizers/meta_optimizer.cc:623] layout: Graph size after: 965 nodes (137), 1222 edges (254), time = 193.217ms.
2019-07-11 07:08:34.901506: I tensorflow/core/grappler/optimizers/meta_optimizer.cc:623] constant folding: Graph size after: 959 nodes (-6), 1222 edges (0), time = 469.334ms.
2019-07-11 07:08:34.901539: I tensorflow/core/grappler/optimizers/meta_optimizer.cc:623] TensorRTOptimizer: Graph size after: 527 nodes (-432), 782 edges (-440), time = 2563.75ms.
```

it means what？ and `time = 2563.75ms`

means the time that the `TensorRTOptimizer`

process costs?